First, decide if this is a good time for both of you to concentrate on the conversation. If either of you is running out of the house on the way to an appointment, being rushed or distracted is not conducive to good communication. Next, decide that you're going to sit back and really listen to what your teen has to say. You're not going to jump in with advice, criticism or judgmental statements. By listening to your teens, you're giving them the message that they're important to you, what they say has value, and that you trust them to have a valid perspective on whatever problem it is that they're bringing up.
Body language that shows your teenager that you're listening includes closing your book or turning off your cell phone; looking at your teenager (eye contact); and nodding or saying "uh huh," while he or she talks. If you want to ask questions, you'll find that open questions ("What else happened?" "Could you give me some examples of that?") encourage your teen to open up more and may give them insight into their behavior, while closed questions (those beginning with "Is," "Are," and "Do") may give you a yes or no answer, but not much more than that.
Active listening is when you reflect back to the teen what was said or what feelings you think were behind the communication: Your teen feels that you've really heard what he or she said, or corrects you if you didn't quite get it right. Paraphrase what your teen said; don't repeat it back verbatim or it can be annoying. Though active listening might not be second nature for you, the more you practice it, the easier it gets -- and the rewards will be quickly evident.